1. Field of the Invention
The invention relates to an output driver for an integrated circuit having a driver circuit for driving an input signal onto an output line. The invention furthermore relates to a method for driving an output driver for an integrated circuit.
2. Description of the Related Art
Integrated circuits usually have output drivers for driving signals which have been generated in circuits of the integrated circuit on external lines connected to the integrated circuit. To define the driver behavior of the output drivers, a specification is provided which, depending on the output driver, provides an upper and a lower current value or an upper and lower potential value depending on the signal state (high level or low level) of the output signal to be driven. In this case, the specification respectively specifies an upper and lower current-voltage characteristic curve for the activated pull-up path of the driver circuit and for the pull-down path of the driver circuit, which characteristic curve in each case defines a current intensity range within which the current intensity through the relevant path and thus through the output line must be. Depending on whether a high or low level is intended to be driven by the output driver, the specification prescribes different upper and lower current-voltage characteristic curves for the pull-up path and the pull-down path.
Usually, the specifications for integrated circuits, in particular for SDRAM and DDR memory circuits, provide a relatively large current intensity range or potential range for the output drivers, so that it is simpler to achieve the specification-conforming current intensity values or potential values for process cut-off values, temperatures and voltages (PVT). The specification-conforming current intensity ranges or voltage ranges of the pull-up paths and pull-down paths may signify great differences with regard to the power consumption depending on the position of the actual potential value or current value within the specification, since more power is required in an upper current intensity range and/or in an upper potential range than if the output signal is in a lower range of the permissible predetermined potential window and/or current intensity window.
However, the exact potential value or current value with which the signal is driven with the aid of the output driver cannot be established from the outset since it is necessary to take account of process deviations, temperature fluctuations and voltage fluctuations which might have the effect that the relevant value is outside the specification-conforming window. Moreover, different loads are possible at the outputs of the integrated circuit, so that this may result in different potential values or current values depending on the connected components or the switching states thereof.